Recording engineers use a central routing terminal, commonly known as "patch bay" or "jack bay" to interconnect electrical input and output signals being transferred between audio equipment in a flexible manner. Using a patch bay, an audio engineer can avoid "hard wiring" equipment components directly together. Instead, "patch cords" connect "jacks" which are the connecting points for the input or output of each components. A patch bay allows the audio engineer to configure and reconfigure the components connections in a custom manner for each project.
Wadhams, Dictionary of Music Production and Engineering Technology 165 (1988) defines a patch bay as,
one or more rows of female input and output jacks, used in conjunction with patch cords to route signals through outboard processing gear, or to reroute signals inside the console itself. PA1 a group of jacks in the patch bay that are connected in parallel. A line-level signal patched into any of these jacks can then be sent to more than one destination by patching from the other jacks into separate devices or inputs. The original signal is thus multiplied or replicated for various uses. Often called a mult for short.
Traditional patch bays route signals from a single source to a single destination or in certain circumstances route a single signal from a single source to multiple destinations. The ability of a patch bay to route a single signal output to multiple inputs is called a "multiple" or just "mult" for short.
Wadhams, supra at 147, defines a multiple as,
FIG. 6 is an illustration of a conventional patch bay 11. The patch bay 11 has four output jacks 112 connected to the outputs of pieces of audio gear (not shown), a four jack mult connection 113 (four jacks wired in parallel) and four input jacks 114 connected to the inputs of audio gear (not shown). In the diagram, patch cords 115 are shown connecting output jack 102 to input jack 105 and output jack 103 to input jacks 107 and 108 using the "mult" facility.
Time division multiplexing, hereinafter "TDM" is a method to transmit multiple channels of information over a single communications medium or channel. TDM divides time into small "slices" and uses the single medium to serially connect consecutive channels of information during consecutive slices of time. The principles of TDM are discussed by Blakeslee, T., Digital Design With Standard MSI and LSI, 261-262 (2nd ed. 1979).
FIG. 7 shows a collection of digital devices connected in a conventional bus transfer arrangement which uses time division multiplexing. In FIG. 7, source address bus 120 defines the source of data and the destination address bus 121 indicates which device D should receive the data. A data bus 122 provides the path for the actual data transfer. A bus controller 123 puts out a series of source and destination addresses to perform the desired signal routing.
FIG. 8 is a functional timing diagram showing how conventional time division multiplexing works. During the first time slice T1, device 102 transfers data to device 105, then in the next slice T2, device 103 transfers data to device 107, and finally during T3, device 103 transfers data to device 108.
The TDM technique has been used in audio engineering to transmit digitally configured audio signals by packing multiple channels of audio data on a single satellite data channel. This is described by Pohlman, K., Advanced Digital Audio, 271-276 (1991).
Bandot, Marie-Dominique, Hardware Design of a Digital Mixer for Musical Applications, Audio Engineering Society, 1987, further describes a digital mixer using time division multiplexing.